Disclaimer: This is my method. Use it or don't it doesn't matter to me. Agree with it or not, again it doesn't matter to me.
Winterization for Carbed Mercruiser V8 or V6.
Note 1: My method below describes how I winterize a marine engine. I personally do not change the engine oil/filter or out drive gear oil in the fall. Have not for 30+ years.
Note 2 : The out drive when it sits all winter in the cold, seals can go bad regardless if pressure checked in the fall or the gear oil is water free. If the drive is not serviced properly in the spring the gear oil could possibly leak causing extensive damage.
Proper out drive Spring Service includes Drain and pressure check and check gimbal bearing and grease any fittings needing grease and new O-rings as supplied in gasket kit and grease the splined drive shaft and the two o-rings on shaft.
My winterization procedure: Done on trailer.
RAW WATER cooled only (not closed/fresh water cooling systems)
Add appropriate amount of Stabil to gas tank.
With Drive Down and allowed to sit for at least 2 hours so if any water present will flow to bottom of outdrive.
Remove lower unit oil fill plug and check for water contamination. If oil looks good reinstall plug. If oil is milky or water comes out, outdrive must be serviced/repaired by (pressure checking) to find bad seal before winter storage.
Hook up water hose to ear muffs and attach to out drive and make sure out drive is lowered almost all the way down.
Turn on water at hose.
Start engine and let run for ~30 minutes at ~ 1000 rpm. (this allows Stable added to gas tank to reach Carb)
Turn engine off. Turn water off and remove ear muffs. (leave out drive down for now)
Remove engine block water plugs, they are on the right side and left sides of engine near center of block and very close to oil pan, Typically Bronze material. (Could be two piece or Single plug, or Plastic winged screw type)
Once the plug(s) have been removed, Poke thru with small screw driver to loosen up all cast and rust so the water flows out in a steady stream.
Remove the plugs in the exhaust manifolds, they are under the manifold ¾ of the way back towards the back of engine, poke it clear so the water comes out in a steady stream.
If Plastic winged type remove them and make sure water flows good. (they could be located where hose attaches at bottom of exhaust manifold)
Remove the two water hoses that go to Elbows at the front of the engine where they attach to the thermostat housing . If No hoses go to elbows, Remove the two hoses at thermostat housing that go to bottom of Exhaust Manifolds
Remove the incoming water hose (the one coming in on the right hand side (oil filter side) that comes from the transom and goes thru the power steering cooler.
Remove the LARGE hose that is U shaped from the engine water/circulating pump to the thermostat housing (remove from the thermostat housing side only and after engine blocks has drained, twist this hose down towards the bilge to drain any remaining water out of this hose.
When the water has drained out of the block and the manifolds reinstall the plugs. DO NOT over tighten them just good and snug.
Have 1 gallon of
RV antifreeze ready, pour ¼ of it into the two hoses that go to elbows or bottom of the exhaust manifolds and it will go directly into the exhaust elbows/manifold.
Pour ¼ of the RV antifreeze into the incoming water hose (SLOWLY) and make sure you hear/see it come out the out drive intake ports!!!
This back flushes the incoming water thru the power steering cooler and the transom assembly thru out drive (you may have to raise the hose up several inches to allow the antifreeze to flow).
Pour the rest of the RV antifreeze into the LARGE hose that was removed from the thermostat housing, this goes straight into the engine.
Reinstall all the hoses and tighten all clamps.
Raise the out drive to trailer position.
Unhook battery and you are done!!
Note 3: When out drive is in the down position it is self draining.
Again, This applies to most V8 and V6 cylinder Mercruiser Carbed engines RAW WATER cooled only (not closed/Fresh water cooling systems)
